This invention relates to a transceiver for communication with a remote station, and, more particularly, to a transceiver which determines an optimal operation mode for such communication and to an antenna system which may be used with such transceiver.
For communication with certain remote stations, a portable and/or mobile transmitter and receiver, or a combination thereof commonly referred to as a transceiver, may be used. A portable transceiver may include a hand-held unit which contains all required transmitter, receiver and antenna components to operate as a stand-alone transmitter of electromagnetic energy to the remote station, and receiver of electromagnetic energy from the remote station, such as a satellite. Generally the electromagnetic energy is intentionally perturbated or modulated in some fashion, for example, by amplitude modulation, frequency modulation, frequency shift keying, or some combination thereof, for facilitating information exchange between the local station and the remote station.
In operation, and especially if moving during operation, a local station mobile transceiver such as may be used in conjunction with a land-based vehicle like a car, train or tank, or an air-based vehicle like an aeroplane, helicopter or jet, or a water-based vehicle like a boat or ship, and especially a portable transceiver that is held in the hand of an operator during operation, will change the orientation of the transmit and/or receive antenna with respect to the respective receive and/or transmit antenna at the remote station. Further, movement of the local transceiver within the local environment, will cause random effects or perturbations, such as reflection and scattering, to affect communication between the local and remote stations due to changes in electromagnetic reflectivity properties of the local environment, both natural e.g., trees, fields, bodies of water, and cultural e.g., buildings, roads, in the vicinity of the transceiver. Even without such movement, local phenomena may sporadically and non-uniformly affect the communication. Such changes in orientation of antennas and/or perturbations are generally manifested in an alteration in the direction of polarization of the transmission and/or reception which ultimately may result in a decrease in detected signal strength along with an attendant increase in the signal to noise ratio.
Multipath fading due to received energy reaching the receiver via a direct path between local and remote stations as well as over a reflected or indirect path emanating, for example, from scattering surfaces including the earth degrades the quality of communication between the local and remote station. For example, the direct and reflected waves of energy arriving at the receiver interfere with each other and instantaneously either reinforce, or add, or detract, or subtract, from each other to form the resultant received energy signal available for processing. Long time interval effects may include changing degrees of such addition and subtraction in a periodic or aperiodic manner, which may be manifested, for example, by additional apparent modulation, such as warbling.
In an existing system, two antennas, each having the same bandwidth are associated with a portable unit. Upon receipt of a test signal from a remote station, electronics associated with the portable unit select the antenna having the higher output to use as the receive antenna during a subsequent communication interval until a next test-tone cycle from the remote station is processed.